* Enable the `async` feature for the `cached` crate
* Make the types that we cache implement `Clone`
* Rename the argument of mixcloud::redirect_url` because of this issue:
https://github.com/jaemk/cached/issues/114
* Use the `thiserror` crate to make our own error type
* Implement Rocket's `Responder` type for the error type
* Adjust all methods to use the error type
* Small documentation tweaks
This might solve some issues with clients that don't get the file type
and size and don't know what to do?
Also, we're not longer involved in the download, yay! (For now.)